Hollow golf club with composite core

ABSTRACT

A golf club having a hollow club head construction with a lightweight composite core inserted into the club head cavity and juxtaposed against a front face by compressed gas to provide support to the front face therein. The core material is less dense and having greater flexibility than the front face. The front face has a variable stiffness so as to create a variable Coefficient of Restitution (COR) across the face, therein normalizing the hitting area over a greater portion of the face. The composite core in cooperation with the front face to provide a COR from about 0.8 in the middle of the face to about 0.9 in the outer section. The body of the club head having at least one opening wherein the composite core is visible and provides the shell for that portion of the club head.

FIELD OF THE INVENTION

[0001] This invention relates to a hollow golf club head having a composite core, and a method of making such a head.

BACKGROUND OF THE INVENTION

[0002] The desire for perimeter weighting in a golf club iron is well known in the art. This desire stems from the fact that as the mass of the club is distributed towards the perimeter, the trajectory of the hit ball becomes more accurate, despite off-center hits away from the sweet spot of the golf club face or hitting surface. Consequently, many modern golf club irons have a rear cavity that extends towards the rear side of the face surface of the iron. The weight saved, by creating a rear cavity in the club, is re-distributed to the perimeter of the golf club head. The greater the volume of the cavity, the greater the amount of mass of metal that can be redistributed to the perimeter of the golf club head.

[0003] Conventionally, golf club heads were made from a single material, usually stainless steel for some metal woods and iron type clubs, and recently a large shift in the use of titanium for metal woods. Carbon fiber composite materials have been introduced in an effort to decrease the weight of the golf club head while subsequently increasing the club head's volume. Composite materials have been used widely to reinforce thin club faces, while providing “feel” and in some instances vibration dampening.

[0004] Typically, in an iron club head, composite inserts are used to support the rear surface of the front face. They are generally sheets of composite attached with an adhesive. The lightweight composite allows for the face to be thin and therefore a larger face and bigger sweet spot.

[0005] It is desirable to provide a golf club that optimizes the moment of inertia (MOI) and also normalizes the ball speed over a large area of the face. Thus the ball is launched at similar speeds over a large region to create a larger sweet zone.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a golf club including a metal and composite body. The body is hollow and comprises a front face, toe section, heel section, sole, top and hosel. The metal portion of the body includes, at least, the front face and preferably includes the toe section, heel section, sole and hosel. The composite material forms the remainder of the body and includes a portion juxtaposed with the front face. Preferably, the composite is molded to abut the front face directly and provide structural support therefore.

[0007] In one embodiment of the invention, a composite core and metallic body are combined to form a hollow golf club head. The composite is used to structurally support a thin front face, and for increased Coefficient of Restitution (COR). Preferably, the front face is of a higher density and lower Young's Modulus than the composite core.

[0008] In an embodiment of the invention the front face is has a first stiffness at the center of gravity (near the center of the face) and becomes progressively more flexible away from the center of gravity. Preferably, the club is designed such that the face provides substantially uniform ball speed from hits at various locations, i.e., it provides an enlarged sweet zone. The COR across the front face varies from about 0.8 to about 0.9 across the front face. The variation in flexibility across the face may be a result of the front face structure alone, or it may result from a combination of the front face and composite core structures or the front face and composite core materials. The internal volume of the golf club iron head is about 35 cc to 50 cc.

[0009] An embodiment of the invention is comprised of a metal body member that may be cast, forged, stamped or made by metal injection molding. The body member is placed in a mold and a composite core is biasly inflated and expanded against the metal body and mold by a bladder method. Preferably, the composite core is located such that the composite material is juxtaposed against portions of the metal body and mold. The mold is used as a boundary for specific regions of the club head where the metal body has an opening(s) such that the exterior of the club is partially metal and partially composite. Embodiments of the invention are provided in both hollow irons as well as metal woods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a rear elevation view of an embodiment of the present invention showing the visible composite core.

[0011]FIG. 2 is a cross-sectional view of the invention of FIG. 1 along line A-A showing the bladder molded composite core

[0012]FIG. 3 is a rear elevation view of the FIG. 1 without the composite core.

[0013]FIG. 4 is a pictorial view of the sole showing the position of a plug.

[0014]FIG. 5 is a front elevation view of FIG. 1.

[0015]FIG. 6 is a cross-sectional view of an embodiment of the invention showing a composite core assembly that was inserted by being pivoted into an opening in the club head.

[0016]FIG. 7 is a top view of a metal wood showing composite core material visual from the crown area.

[0017]FIG. 8 is a cross section view of FIG. 7 along line B-B.

DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of an iron golf club head 10 of the present invention is shown in FIGS. 1 to 5. The body 12 of the golf club head 10 has a metal portion having a face section 14 providing a front face 16 for striking golf balls, a top section 15, a sole 17 having an open port 19, a hosel 21, a thin front region 23 of the sole 17, and a rear opening 25. A sole plug 26 is inserted within the port 19, as discussed later. The body 12 has a cavity 22 that is defined rearward of the face section 14. A lightweight composite core 20 is biasly placed within the cavity 22, juxtaposed against a rear surface 18 of the body 12, to internally reinforce the body 12, and also support the front face 16. The metal body 12 may be cast, forged, stamped or made by metal injection molding process. Reinforcing the body 12 with the lightweight composite core 20 allows for the body 12 to be thinned down in select regions. The thinned down regions permit the mass distribution optimization (Center of Gravity and Moment of Inertia) of the club head 10, and also stiffening the front face 16 that may be relatively flexible due to the thin structure.

[0019] The front face 16 can be made relatively thin because of the reinforcement of the composite core 20. The thickness (t₁) of the front face 16 is preferably between about 0.04 inch to 0.12 inch, and more preferably between 0.06 inch to 0.1, while the thickness (t₂) of the composite core 20 is preferably between about 0.02 inch to 0.1 inch. The composite reinforced face can be designed to provide face flexibility characteristics that yield maximum Coefficient of Restitution (COR) values from about 0.8 to about 0.9. The COR of the club head 10 may vary across the front face 16 to normalize ball speed and provide an enlarged sweet zone for added forgiveness. Therein the COR of the club 10 of the present invention may be about 0.8 at the face center and greater than 0.8 away from the face center. Generally, the stiffness of the front face 16 is greatest at the face center, and becomes progressively more flexible away from the face center. The coefficient of restitution is obtained under test conditions, such as those specified by the USGA. The standard USGA conditions for measuring the coefficient of restitution is set forth in the USGA Procedure for Measuring the Velocity Ratio of a Club Head for Conformance to Rule 4-1e, Appendix II available from the U.S.G.A.

[0020] The club head 10 forms a hollow style club 10 with thin walls in select regions, especially the face side section 14. The thin regions are the structurally reinforced with the lightweight composite core 20. The composite core 20 may be made of plastic, carbon graphite or any lightweight material with a density less than 4.5 gm/cc, and may be inserted into the hollow golf club 10 in a variety of methods. While the method of inserting the composite core 20 may vary, one example of the invention uses a well-known bladder method. This method comprises a composite core 20 being inserted into the cavity 22, and a bladder (not shown), preferably made from latex, silicone, or similar materials, is then introduced into the composite core 20 and therein into the cavity 22, through a port 19 (shown in FIG. 1). Preferably, the composite core 20 is located such that the composite material is juxtaposed against portions of the metal body 12 and the mold. The assembly comprises, the metal golf club body 12, composite core 20, and bladder. It is then positioned in a mold, which is not shown, but is used as a boundary for specific regions of the club head 10 where the metal body 12 has an opening, such as the rear opening 25. Thus, the exterior of the resultant club head 10 is partially metal and partially composite. A source of pressurized gas, usually air, (source not shown) is introduced through the port 19 to inflate and expand the bladder, and thereby cause plies of the composite core 20 to biasly expand against the inner walls of the golf club 10 and against the internal walls of the mold. The internal walls of the tool are thus used as a boundary for a region of composite or plastic that is visible to the outside of the golf club 10. Heat may be provided at a predetermined temperature for a selected period of time, i.e., a time sufficient to allow proper curing of the composite material. After depressurizing, the bladder may be removed through the port 19, and the golf club head 10 may be removed from the mold. The exterior of the resultant club head 10 is partially metal body 12 and partially composite core material 20 with an internal volume between about 35 cc to 50 cc.

[0021] The introduction of the plug 26 in the port 19 causes the center of gravity of the club head to be lowered. Plugs 26 of varying weight can adjust the swing weight of the club to match a golfer's specifications. An embodiment of the invention used a plug 26 made from tungsten.

[0022] While embodiments of the present invention focus on irons, FIGS. 7 to 8 depict a typical metal wood 50 that has been manufactured by this method and wherein composite core material 54 shows through at the crown section 52. The hollow cavity of the metal wood 50 provides for an internal volume between about 300 cc to 400 cc. Fairway wood versions of this metal wood 50 have internal volumes between about 150 cc to 225 cc.

[0023] In another embodiment of the invention as depicted by FIG. 6, an iron type club head 40 is formed from a cast body 41 having an open section 43, and a separately formed sub-composite core assembly 42, which is first formed, then inserted and securely received into the cavity 22 of the club head 40. Insertion of the assembly 42 into the cavity 22 may require an injection or compressive tool. Preferably, after it has been substantially formed and cured, the composite core assembly 42 is pinched and pivoted into the open section 43, then it adheres to the inner wall 46. Opening 43 is then closed by the structure of the core assembly 42. The core assembly 42 supports a substantial portion of the front face 47 and is secured to the inner wall 46 by a layer of adhesive 45. The composite core assembly 42 may have structural means 49 to snap-fit into position with the club head body 12. After being positioned into place, the opening 48 around the core assembly 42 is sealed by an epoxy.

[0024] The construction of the front face 16, as shown in FIG. 5, illustrates an example of the present invention comprising a variation in the thickness of the front face 16. The front face 16 is preferably partitioned into oval regions, each having a progressively lower stiffness. Thus, moving away from the face center, the front face 16 decreases in stiffness and thus increases in flexibility, therein increasing the COR in that area. This design normalizes ball speed over a large range, thus improving the golf club's “forgiveness” or enlarged sweet spot. The front face 16 may be made such that it's flexibility in the face center (proximate the location of the CG) is generally stiffer than the area around the face center. The increase in COR in combination with the energy loss, that occurs from missing a direct central hit on the front face 14, balances out to thereby give the same ball speed as a shot hit directly in line with the face center. While it is known that variable face flexibility can be achieved by making adjustments in the thickness of the front face 16, an example of the invention accomplishes the varying of flexibility by incorporating a varying composite stiffness (via geometry or material variations).

[0025] It is believed that those skilled in the pertinent art will recognize the improved inventive concepts of this invention. And they will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention. 

What is claimed is:
 1. A golf club head comprising: a body made of a first material having a front face of variable stiffness, and a rear cavity extending rearward from the front face; a composite core comprised of a second material less dense and more flexible than the first inserted into the rear cavity; and the composite core inflated and expanded by a pressurized gas wherein at least a portion of the composite core biasly juxtaposes against the front face to form a hollow body having an internal volume between 35 cc to 50 cc.
 2. The club head of claim 1, wherein the composite core is made from a lightweight material such as plastic or carbon graphite.
 3. The club head of claim 2, wherein the composite core material has a density equal or less than 4.5 gm/cc.
 4. The club head of claim 1, wherein the stiffness of the front face is greatest at the face center, and becomes progressively more flexible away from the face center.
 5. The club head of claim 1, wherein the Coefficient of Restitution varies across the front face to normalize ball speed and provide for an enlarged sweet zone.
 6. The club head of claim 5, wherein the maximum Coefficient of Restitution, ranges between about 0.8 to about 0.9.
 7. The club head of claim 1, wherein the pressurized gas is air.
 8. The club head of claim 1, wherein the rear cavity comprises an opening that is sealed by a visible portion of the composite core.
 9. The club head of claim 1, wherein the elasticity of the material of the composite core may cooperate with the front face to create a varying COR across the front face for normalizing ball speed and creating an enlarged sweet zone. 10-22. (Cancelled) 